How to address structure offset intentions correctly

[hellow554]

I try to "decompile" a popular SNES game and often the code looks something like this:

struct Player_t $8000
  .x: skip 1
  .y: skip 1
endstruct

LDX.W #Player_t ; base address of an struct array
LDA.W $01, X ; use the second byte of that struct

Of course these don't stand next to each other and often it is assumed that X points to an struct in that array.

I can think of two possibilities. What other ideas do you have in mind?

1. This one would make the lowest effort to change something (just "invent" an offsetof macro or function): LDA.W offsetof(player.Y), X
2. This one would require more modification to the base, but makes then intention much clearer IMHO: LDA.W player[X].y, but I'm not sure how other would find this, because it lacks the , X in the end which has moved into the array index. Second X is now not an array index, but an offset from $0.

What do you have mind to make the intention more clear that the original example?

[RPGHacker]

An offsetof() does sound like a reasonable addition to Asar (though I'm not sure how easy it is to add - don't remember how exactly struct labels are stored in Asar).

For the time being, I'd propose a workaround similar to this:

PlayerData = $8000
struct Player_t
  .x: skip 1
  .y: skip 1
endstruct

LDX.W #PlayerData ; base address of an struct array
LDA.W Player_t.y, X ; use the second byte of that struct

[hellow554]

I didn't know that you can omit the address on a struct. The documentation says otherwise ;)
I'll try it out and get back to you

[hellow554]

common/structs.asm:31: error: (Ebank_border_crossed): A bank border was crossed, SNES address $000001.
    in block: [.pos_x: skip 2]

Because the structs.asm file is included becfore the first ORG or BASE command, the error pops up.

I inserted a dummy BASE $8000 and it works now, but it feels hacky....

[RPGHacker]

I thought it was a thing, but maybe I misremembered. If it doesn't work, I guess you could also do

struct Player_t $000000
  .x: skip 1
  .y: skip 1
endstruct

It's what I use in VWF Dialogues, and it doesn't seem to throw bank border errors. Example can be seen here:
https://github.com/RPGHacker/SMW-Workspace/blob/master/patches/shared/shared.asm
in the define_enum() macro.